1. Field of the Invention
The present invention relates generally to magnetic tape transport apparatus. More particularly, the invention relates to compensation for head-to-tape stick-slip action in transport apparatus of the type having a single, speed-regulated capstan for metering magnetic tape into and out of a magnetic transducer station.
2. Description Relative to the Prior Art
There is known in the prior art magnetic tape transport apparatus of the type having a single, speed-regulated capstan that serves for metering magnetic tape into and out of a magnetic head transducer station. For this to be accomplished with a single capstan drive, a turnaround roller serves to effect a 180-degree change in the direction of the magnetic tape after the capstan initially feeds the tape through the transducer station for a recording operation. After the direction of tape is reversed, the capstan then pulls the tape back through the transducer station for a playback operation.
The transducer station and the turnaround roller, with the two tape spans therebetween, constitute a resonant system. With the inertia of the turnaround roller being excited by a stick-slip action of the tape as it is drawn over a magnetic head, the flexible magnetic tape can resonate at oscillation frequencies in the range of 350 hertz (Hz). These frequencies fall within the flutter compensation range required of a modern magnetic tape recorder.
In the prior art, rotary damped vibration absorbers have proven only partially successful in reducing the turnaround roller inertia. Furthermore, vibration absorbers introduce phase distortion which adversely affects servomechanism control of the capstan.
Separate motors, servo controlled from the same source, have driven the capstan and turnaround roller. This has proven to be very expensive and requires an exact match between the respective diameters of the capstan and roller. Unequal circumferences generate excess tension on one side or the other of the tape loop, with consequent slipping on the capstan and/or stretching of the tape.